Why DNS change works on landline but not on mobile data

[moto1860]

Let me elaborate title
My country ISPs have a block to foreign betting sites, changing DNS to my landline does the trick and I can reach them no problem, however this doesn't work when I use my cell as a hotspot and I change DNS to that connection from my laptop.
The cell is not rooted so I haven't changed DNS on my cell but I don't think that's the issue as of course the cell does connect to such sites under LAN wi-fi, it doesn't when on mobile data. Hope it's all clear.

[TheFu]

Use a VPN.

[moto1860]

Yes, I'm using a VPN tho that only works on cell phone, can't use VPN in tethering. From what I am reading you can't change DHCP settings of wifi tethering, maybe be the same for DNS.
Anyways I used DoH on FF to work around this problem on the laptop. Couldn't manage to set DoH on chromium, nor chrome, I don't have the options listed in the tutorials I've seen online.